1. Field of the Invention
The present invention relates to the electrochemical production of alkylene oxides and particularly to a process wherein an alkylene oxide is produced at both the anode and cathode of an electrochemical reactor.
2. Description of the Prior Art
The production of alkylene oxide is of very great commercial importance. Ethylene oxide is produced commercially by the silver catalyzed vapor phase oxidation of ethylene with molecular oxygen.
Propylene oxide is produced commercially by the catalytic reaction of propylene with an organic hydroperoxide, see basic U.S. Pat. No. 3,351,635, or by the chlorohydrin process technology.
Research continues in an effort to develop still further improved processes for the production of alkylene oxides, and there have been efforts to apply electrochemical reaction procedures to alkylene oxide production. For example, U.S. Pat. No. 3,427,235 describes the electrochemical production of olefin oxides in an electrochemical cell by passing current through an aqueous medium to generate oxygen with the thus generated oxygen reacting with olefin to produce the oxirane compound.
U.S. Pat. No. 3,635,803 relates to the production of propylene oxide by electrochemical means using an aqueous medium containing an acetate as electrolyte.
U.S. Pat. No. 3,723,264 relates to electrochemical oxidation of an olefin using a diaphragm-compartmented electrolytic cell with an asbestos diaphragm.
U.S. Pat. No. 4,119,507 relates to electrochemical oxidation of an olefin using an aqueous alkali metal chloride electrolyte with olefin chlorohydrin formation.
UK Patent 1,467,864 relates to electrochemical oxidation of propylene to propylene oxide in an undivided cell having an aqueous solution of water soluble chloride or bromide. Electrode spacing is 0.05 to 2 mm and current densities of 1 to 100 A/dm.sup.2 are used.
U.S. Pat. No. 3,497,431 relates to electrochemical production of olefin oxides in an electrochemical cell with the anode and cathode separated by an interposed diaphragm with the hydrostatic pressure in the anode compartment higher than that in the cathode compartment.
U.S. Pat. No. 4,634,506 relates to electrochemical oxidation of olefin to olefin oxide where aqueous electrolyte and olefin are mixed under pressure and are passed through a restriction device to reduce pressure and vaporize the olefin.
U.S. Pat. No. 4,270,995 relates to an electrochemical cell having an upper and lower chamber divided by a perforated plate suitable for the production of propylene oxide.
Holbrook, et al., "Electrooxidation of Olefins at a Silver Electrode", Journal of Catalysis, 38, p. 294-298 (1975) describe the electrochemical oxidation of olefins to olefin oxides.
Van der Eijk, et al., "Electrochemical Epoxidation of Olefins", Catalysis Today, 3, p. 259-266 (1988) describe the oxidation of olefins to epoxides by reaction of olefins with electrochemically generated silver (II)--pyridine ions.
Oduoza, et al., "Aspects of the Direct Electrochemical Oxidation of Propylene", Chem. Eng. Symp. Series, 127, p. 37-47 (1992), describe the direct anodic oxidation of propylene to propylene oxide and glycol in an alkaline electrolyte in batch and sieve plate bipolar flow cells.
Chou, et al., "Anodic Oxidation of Propylene on a Screen Electrode", Chem. Eng. Sci, 35, p 1581-1590 (1980) describe the oxidation of propylene to propylene oxide on a screen anode in aqueous solution of a pH of 12.0-13.9.
Scott, et al., "Pilot Scale Electrosynthesis of Alkene Oxides by Direct and Indirect Oxidation in a Sieve Plate Electrochemical Reactor", Chem. Eng. Sci., 47, No. 9-11, p. 2957-2962 (1992), describes the electrosynthesis of alkene oxides in a sieve plate electrochemical reactor.
Japanese Kokai No. 6-220033 describes the production of alkylene oxides from olefin and oxygen through the use of a fuel cell system with hydrogen fed to the anode chamber and olefin and oxygen fed to the cathode chamber. Alkylene oxide is produced in the cathode chamber.
Otsuka, et al., "Simultaneous Epoxidation of 1-Hexene and Hydroxylation of Benzene During Electrolysis of Water", Chemistry Letters, p. 1861-1864 (1994) describe a system for simultaneous epoxidation of 1-hexene at the anode and the hydroxylation of benzene at the cathode during the electrolysis of water. Otsuka also anodically epoxidized cyclohexene in a fuel cell system, the oxygen being abstracted from water at the anode. The highest current efficiency was 4.5%, at 47.6% selectivity to the epoxide. The cathode chemistry is proton reduction to hydrogen gas. See "Epoxidation of Cyclohexene with the Nascent Oxygen Generated by electrolysis of Water", K. Otsuka, M. Yoshinaka and I. Yamanaka, J. Chem. Soc., Chem. Commun., (1993), p. 611-612. Oxidation of toluene to benzaldehyde by Mn.sup.3+ and OH free radicals, generated in the anodic and cathodic reactions, respectively, was carried out simultaneously in the cathodic and anodic compartments of a cell. The selectivity of benzaldehyde was very high in both the anodic and cathodic reactions. The maximum total current efficiency for benzaldehyde production in the paired electrooxidation was 171%. See "Paired Electrooxidation. I. Production of Benzaldehyde", J. J. Jow, A. C. Lee, T. C. Chou, J. Appl. Electrochem., vol, 17, (1987), p. 753-759.
In hydrogen peroxide production, the consumption of anode by product oxygen at the cathode is known. See for example, "Processes for the Production of Mixtures of Caustic soda and Hydrogen Peroxide via the Reduction of Oxygen", P. C. Foller, R. T. Bombard, J. of Applied Electrochemistry, vol. 25 (1995). p. 613-627.